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Ecosystem Processes-I (Part-2) Paper No. : 12 Principles of Ecology Module : 30: Ecosystem: Ecosystem Processes-I (Part-2) Development Team Principal Investigator: Prof. Neeta Sehgal Head, Department of Zoology, University of Delhi Co-Principal Investigator: Prof. D.K. Singh Department of Zoology, University of Delhi Paper Coordinator: Prof. D.K. Singh Department of Zoology, University of Delhi Content Writer: Dr. Kapinder Kirori Mal College, University of Delhi Content Reviewer: Prof. K.S. Rao Department of Botany, University of Delhi 1 Principles of Ecology ZOOLOGY Ecosystem: Ecosystem Processes-I (Part-2) Description of Module Subject Name ZOOLOGY Paper Name Principles of Ecology Module Name/Title Ecosystem Module Id 30: Ecosystem: Ecosystem Processes-I (Part-II) Keywords Ecological energetic, Ecological efficiency, Y-shaped energy model, linear energy flow model, Universal energy flow model. Contents 1. Learning Outcomes 2. Introduction 3. Ecological energetic 4. Thermodynamics principle 4.1. Ist law of thermodynamics 4.2. IInd law of thermodynamics 5. Lindeman trophic dynamic concept 6. Assimilated energy and respiration energy 7. Ecological efficiency 8. Models of energy flow in ecosystem 8.1. Single channel energy flow model 8.2. Y-shaped or double channel energy flow model 8.3. Universal energy flow model 9. Ecosystem goods and services 10. Homeostasis in ecosystem 11. Control on ecosystem function 12. Summary 2 Principles of Ecology ZOOLOGY Ecosystem: Ecosystem Processes-I (Part-2) 1. Learning Outcomes After studying this module, you shall be able to Understand the concept of ecological energetics and laws of thermodynamics. Describe the assimilation energy and ecological efficiency in the ecosystem. Understand energy flow in the ecosystem. Describe various models to explain energy flow. Explain ecosystem services and ecosystem homeostasis. Explain mechanism of control of ecosystem function. 2. Introduction Energy can be defined as the capacity to do work. All biological activities need consumption of energy which ultimately derives from the sun. The solar energy is converted into chemical energy by the process of photosynthesis which is stored in plant tissues and then transformed into mechanical and heat energy during metabolic activities. In the biological world, the energy flows from the sun to plants and then to all heterotrophic organisms, such as microorganisms, animals and human (figure 1). Heat energy (metabolism) Chemical energy Solar radiation Consumers Sun Producers (metabolism) Decomposers Chemical energy (metabolism) Heat energy Heat energy Figure.1: Energy flow from sun to plant and then to all heterotrophic organisms. 3 Principles of Ecology ZOOLOGY Ecosystem: Ecosystem Processes-I (Part-2) Mechanical energy is present in two forms, kinetic energy and potential energy. Kinetic energy can be defined as the energy possess by the body by virtue of its motion. It is measured by the amount of work done in bringing the body at rest. The potential energy is the stored energy which becomes useful after conversion into the kinetic energy. All organisms require a source of potential energy, which is found in the chemical energy of food. The oxidation of food releases energy which is used to do work. Thus, chemical energy is converted into mechanical energy. Food is the means to transfer of both matter and energy in the living world. The unit of measurement of energy is Joule. All forms of energy can be completely converted into heat energy. Heat is measured in calories. One calorie is equal to the heat energy required to raise the temperature of 1 gram of water from 14.5°C to 15.5°C, and one calorie is equal to 4.2 joules. 3. Ecological energetics Ecological energetics consists of energy transformation which occurs within the ecosystems. Ecological energetic consists of: i) The amount of energy reaching to an ecosystem per unit of area/per unit of time. ii) The quantity of energy trapped by green plants which they converted into chemical energy (photosynthesis). iii) The quantity and energy flow from producers to organisms of different trophic levels (consumers) over a period of time in given area. The energy used by all green plants derived from solar radiations. Only a small fraction of energy reaches to earth’s surface (1 to 5%) is used by green plants for photosynthesis and rest is absorbed as heat by ground vegetation or water. In fact, only about 0.02% of the sunlight reaching the atmosphere is used in the process of photosynthesis. 4. Thermodynamics Principle 4 Principles of Ecology ZOOLOGY Ecosystem: Ecosystem Processes-I (Part-2) Energy transformation in ecosystems can also be explained in relation to the laws of thermodynamics, which are usefully applied to closed systems. 4.1. Ist Law of thermodynamics (law of conservation of energy) It state that in a closed system, energy can neither be created nor destroyed but can only be transferred from one form into another. When fuel is burnt to drive a car, the potential energy in chemical bond of fuel is converted into mechanical energy to drive the car. The key point is, the total amount of energy consumed and compare with the total amount of energy produced would always be equal. Such type of energy conservation is also found in biological system. In ecological systems solar energy is converted into chemical energy stored in food materials which is ultimately converted into mechanical and heat energy. Thus, in ecological systems, the energy is neither created nor destroyed but is converted from one form into another. Thus, when wood is burned the potential energy present in the molecules of wood equals the kinetic energy released, and heat is evolved to the surroundings. This is an exothermic reaction. In an endothermic reaction, energy from the surrounding may be paid into a reaction. For example, in photosynthesis, the molecules of the products store more energy than the reactants. The extra energy is acquired from the sunlight, but even then there is no gain or loss in total energy. 4.2. IInd Law of thermodynamics The second law of thermodynamics states that processes involving energy transformation will not occur spontaneously unless there is degradation of energy from a non-random to a random form. In other words, the disorder (entropy) in the universe is constantly increasing and that during energy conservation, an energy transformation will spontaneously occur unless there is degradation of energy from a concentrated form into a dispersed form. For example, in man-made machines (closed systems), heat is the simplest and most recognizable medium of energy transfer. The outcome of this law is very significant in biological system. But in biological systems, energy transfer is not a useful medium, as the living systems are fundamentally isothermal and there is no significant variation in temperature between different cells in the organism or between various cells in a tissue of the organism. At each level of conservation, some of the energy is lost as heat. Therefore, the more conservation 5 Principles of Ecology ZOOLOGY Ecosystem: Ecosystem Processes-I (Part-2) taking place between the capture of light energy by plants and the trophic level being considered, the less the energy is available to that level. The efficiency of the transfer of energy along food chain from one trophic level to another is generally less than 10 percent as the 90 percent of energy is lost as heat. The study of energy flow is important in determining limits to food supply and the production of all biological resources. The capture of light energy and its conversion into stored chemical energy by autotrophic organisms provide ecosystems with their primary energy source. The total amount of energy converted into organic matter is the gross primary production varies between different systems. The energy stored in the food material is made available through cell respiration. Chemical energy is released by burning the organic compound with oxygen using enzyme mediated reactions within cells. It produces carbon dioxide and water as waste products. Energy flow is the movement of energy through a system from an external source through a series of organisms and back to the environment. At each trophic level within the system, only the small fraction of the available energy is used for the production of new tissue. Most is used for respiration and body maintenance. 5. Lindeman’s trophic-dynamic concept According to Lindeman (1942), the amount of energy at trophic level is determined by the net primary production (NPP) and the efficiency at which food energy is converted into biomass. The plants use 15 to 70 percent of assimilated energy for the maintenance which is not available to the consumers. The herbivores and carnivores are comparatively more active as compare to plants which uses more assimilated energy for the maintenance. So, the productivity at each trophic level lies between 5 to 20 percent that of the level below it. The percentage of energy which is transferred from one trophic level to the next trophic level is called as ecological efficiency. In general, secondary producers utilize 55% to 75% of assimilated energy in maintenance. Temperature and moisture are two components of the habitat and the type of species determine the maintenance cost. The dry and hot regions require higher maintenance cost, irrespective of the species. For example, the average maintenance cost of few Indian 6 Principles of Ecology ZOOLOGY Ecosystem: Ecosystem Processes-I (Part-2) earthworm species was 6.48, 9.96 and 20.54 kJ/g dry tissue/ month in the winter, rainy and summer seasons respectively in tropical pastures. The maintenance cost varies seasonally and higher was found in summer which was three times more as compare to winter. 6. Assimilated energy and respiration energy When the organism eats the food, the digestion and absorption of the food is referred to as assimilated energy, which is used for maintenance, building the tissues or it is removed or excreted in unusable metabolic byproducts.
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